1. Field of the Invention
The present invention relates to tabbed sheet support unit which is used to feed a tabbed sheet, a sheet feeding apparatus, and an image forming apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus such as a printer and a copying machine includes a sheet feeding apparatus feeding a sheet one by one from a sheet storage portion in which plural sheets are stored. For example, Japanese Patent Application Laid-Open No. 7-196187 discloses an air sheet feeding system sheet feeding apparatus in which plural sheets are floated by spraying air on an end part of a sheet bundle supported by a lifting and lowering tray and only one sheet is drawn onto a suction conveying belt provided above.
FIG. 10 illustrates an example of the air sheet feeding system sheet feeding apparatus. As shown in FIG. 10, a lifting and lowering tray 12 on which plural sheets S are stacked and supported is provided in a storage case 11. The storage case 11 is of a sheet storage portion in which the sheets S are stored.
When the sheet S are set on the tray 12, positions of the sheets S are retained at an end (hereinafter referred to as front end) on a downstream side in a sheet feeding direction by a front-end regulating plate 17, and the positions of the sheets S are retained at an end (hereinafter referred to as rear end) on an upstream side in the sheet feeding direction by a rear-end regulating plate 13. The positions of the sheets S are also retained at both side ends in a direction (hereinafter referred to as width direction) orthogonal to the sheet feeding direction by a side regulating plate 14.
A suction conveying portion 20 and an air spraying portion 30 are provided above the storage case 11. The suction conveying portion 20 draws and conveys the sheet S. The air spraying portion 30 sprays the air on the end part of the sheet bundle on the tray to float the plural sheets S, and the air spraying portion 30 separates the sheets S one by one.
The suction conveying portion 20 includes a suction conveying belt 21, a suction fan 36, a suction duct 22, and a suction shutter 37. The suction conveying belt 21 is wrapped about a belt driving roller 41, and the suction conveying belt 21 draws the sheet S to convey the sheet S in a right direction of FIG. 10. The suction fan 36 generates a negative pressure in order to cause the suction conveying belt 21 to suck the sheet S. The suction duct 22 is disposed inside the suction conveying belt 21, and the suction duct 22 draws the air through suction holes made in the suction conveying belt 21. The suction shutter 37 is provided between the suction fan 36 and the suction duct 22 in order to turn on and off a suction operation of the suction fan 36.
The air spraying portion 30 includes a loosening nozzle 33, a separation nozzle 34, a separation fan 31, and a separation duct 32. The loosening nozzle 33 and the separation nozzle 34 spray the air on an upper part of the stored sheet bundle. The separation duct 32 supplies the air from the separation fan 31 to the loosening nozzle 33 and the separation nozzle 34.
Part of the air drawn in a direction of arrow C by the separation fan 31 passes through the separation duct 32, and the part of the air is sprayed in a direction of an arrow D through the loosening nozzle 33 to float several sheets in the upper part of the sheet bundle supported on the tray 12. The remaining air is sprayed in a direction of an arrow E through the separation nozzle 34, and the remaining air individually separates the top-most sheet in the several sheets floated by the loosening nozzle 33 and presses the top-most sheet against the suction conveying belt 21.
Frequently the sheet feeding apparatus is adopted for a high-speed machine which can feed 70 A4-size sheets or more per minute. The tray 12 includes a mechanism in which a driving unit (not illustrated) lifts and lowers the tray 12 in a vertical direction while keeping the tray 12 substantially horizontal.
FIG. 11 is a plan view illustrating the detailed storage case 11. Referring to FIG. 11, the rear-end regulating plate 13 which regulates the sheet rear end is disposed while being movable in parallel with the sheet feeding direction illustrated by an arrow H, and the side regulating plates 14 and 16 which regulate the sheet side ends are disposed while being movable in the sheet width direction illustrated by an arrow V.
Thus, the rear-end regulating plate 13 and the side regulating plates 14 and 16 are movably disposed so that a minimum-size sheet SS to a maximum-size sheet LS can be stacked and supported on the tray 12. In order not to obstruct the movement of the side regulating plate 14, the rear-end regulating plate 13 is disposed so as to be movable only in a central part in the width direction of the tray 12.
Recently, in the image forming apparatus, a demand for producing a brochure is increased, and sometimes a sheet in which a tab is attached to an end part thereof (hereinafter referred to as tabbed sheet) is used. Therefore, it is necessary to feed the tabbed sheet from the sheet feeding apparatus, and it is also necessary to be able to feed the tabbed sheet in the air sheet feeding system sheet feeding apparatus.
FIG. 12 illustrates a state in which tabbed sheets TS having given sizes are set in the air sheet feeding system sheet feeding apparatus. In FIG. 12, the tabbed sheets TS are supported by the tray 12 while tabs TSa are located on the upstream side in the sheet feeding direction, the side regulating plates 14 abuts on the side ends of the tabbed sheets TS, and the rear-end regulating plate 13 abuts on the tabs TSa of the tabbed sheets TS.
When the feeding operation is started, the air is sprayed on the front-end sides of the tabbed sheets TS from the loosening nozzle 33 and the separation nozzle 34 as illustrated in FIG. 13. At this point, because the rear-end regulating plate 13 is provided only in the central part, some of the tabbed sheets TS in which the rear-end regulating plate 13 does not abut on the tabs TSa, for example, the top-most and second tabbed sheets TS are moved rearward up to a width TD of the tab TSa in a direction of an arrow T.
The tabbed sheets TS whose tabs cannot be regulated by the rear-end regulating plate 13 are away from the loosening nozzle 33 when moved rearward, which weakens a wind pressure against the tabbed sheets TS. Therefore, as shown in FIG. 14, for example, front-end parts TF of the top-most and second tabbed sheets TS1 and TS2 whose tabs cannot be regulated by the rear-end regulating plate 13 are insufficiently floated and bent. As a result, the air sprayed from the loosening nozzle 33 hardly enters a gap between the sheets, and the sheet front end cannot properly be loosened.
Because the top-most and second tabbed sheets TS1 and TS2 are unstably floated, other sheets also becomes unstable floating states by the influence of the unstable top-most and second tabbed sheets TS1 and TS2, and therefore the other sheets repeat vertical movement in a direction of an arrow R as illustrated in FIG. 14. The generation of the floating state illustrated in FIG. 14 causes troubles such as multi feed, a jam due to a failure of suction to the suction conveying belt 21, and generation of a folded sheet corner.
The feed of tabbed sheets is needed not only in the air sheet feeding system sheet feeding apparatus but also a sheet feeding apparatus having a configuration in which the sheet is fed by a roller while the tray on which the sheets are stacked is lifted and lowered by a lifter mechanism.
However, in the sheet feeding apparatus in which the sheet is fed by the roller, similarly to the air sheet feeding system sheet feeding apparatus, the tab cannot be regulated by the rear-end regulating member, and sometimes the sheet is shifted rearward. In such cases, when the roller which delivers the sheet is disposed on the front end side of the sheet, the sheet cannot be delivered, which sometimes causes a failure of the sheet feed. Even if the sheet can be delivered, because timing at which the sheet is delivered is largely shifted, an interval between the sheets is broadened to lower the productivity or to generate a risk of detecting delay jam.
In order to solve the problem, for example, Japanese Patent Application Laid-Open No. 2000-229732 discloses a technique in which a tab guide dedicated to the tabbed sheet is optionally attached so as to abut on all the tabs TSa of the tabbed sheets TS.
However, in the air sheet feeding system sheet feeding apparatus, it is necessary to attach the tab guide dedicated to the tabbed sheet to an upper surface of the tray 12. When a tab guide 13M as illustrated in FIG. 15 is provided, because areas shown by oblique lines of the tab guide 13M overlap the tray 12, the tab guide 13M cannot be fixed to the storage case 11. That is, it is necessary that the tab guide which abuts on all the tabs TSa of the tabbed sheet TS be attached to the upper surface of the tray 12.
As illustrated in FIG. 16, the tabbed sheet TS is fed, the tray 12 is lifted according to the decrease in the residual sheet, and the tab guide 13M is lifted along with the tray 12. Even if the tab guide 13M is lifted, in order that the tab guide 13M collides with a component 40 constituting the image forming apparatus body, it is necessary to suppress a height of the tab guide 13M.
However, when the height of the tab guide 13M is decreased as illustrated in FIG. 16, a height in which the tab guide 13M can guide the tabbed sheet TS is decreased, and an amount of tabbed sheet TS stacked on the tray 12 is largely decreased. Accordingly, the number of supply times of the tabbed sheets TS is increased, which remarkably deteriorates apparatus operability and productivity.